Hello,
To All, I need help from expert, I want to install 32bits Linux OS on Raspberry Pi 3 B+, Actually I have some customize apps which is working only in 32bits Linux OS like CentOS 6.10 32bits, so I want to use those customize apps also in Raspberry Pi 3 B+ & 4 as well, Please if there any way to do let me know, waiting for your helpful reply, T.I.A

Hello,
To All, I need help from expert, I want to install 32bits Linux OS on Raspberry Pi 3 B+, Actually I have some customize apps which is working only in 32bits Linux OS like CentOS 6.10 32bits, so I want to use those customize apps also in Raspberry Pi 3 B+ & 4 as well, Please if there any way to do let me know, waiting for your helpful reply, T.I.A

The Raspbian OS supplied for the Pi is 32-bits. It is based on Debian.

Thanks for your fast reply, are you sure that its 32bits & I can run my custom apps which I am able to do in CentOS 32bits

If you spend some time on this forum, you will see many posts about Raspbian being 32-bits when the modern Pi hardware is 64-bit capable. (because the RPF want to support all Pi's with one single OS, and the older Pi's (and the Zero) are 32-bit only ARMv6 hardware).

Cant say about the CentOS apps, best if you just try them. The software would be pretty poor if it was intentionally written specifically for one distro.

You will need x86 emulator to run x86 programs on the RPI computer, the RPI computer uses ARM CPU's, people have tried to run x86 programs on the RPI before, yes you can run the x86 software on the RPI computer and the release of the RPI4 with additional ram should improve performance with the emulators, I've seen videos of StarCraft running on the RPI computer, I wouldn't say the x86 emulator would replace a ARM based operating system if you are interested in x86 emulators here is a outdated guide that explains how to install WINE on the RPI computer: